Heretofore, a number of researches have been conducted for achieving a compact ceramic filter with a high filtration area, and proposals have been made of monolithic ceramic filters having a honeycomb structure.
With the monolithic ceramic filters, the filtrate produced on filtration by a filtration membrane formed on the surface of the supply liquid passages flows within the partition walls towards an outer wall of the filter before being discharged out of the filter at the outer wall of the filter. Thus the flow volume of the filtrate within the partition wall becomes larger as the outer wall is approached.
With conventional ceramic filters, having the honeycomb structure, the partition wall has a constant wall thickness. Consequently, the flow rate of the filtrate within the partition wall is increased significantly at a region close to the outer wall, so that the flow resistance to the filtrate is increased significantly to limit the speed of filtration. Consequently, a ceramic filter having a larger filtration area has been difficult to put into practice on the industrial scale.
As solutions to this problem, crossflow ceramic filters having filtrate conduits as disclosed in JP Patent KOHYO Publication (National laying-open of PCT international application) Nos. 01-501534 (WO 88/07398) or 03-500386 (WO 90/03831), have been proposed.